12 



BULLETIN" 620, U. S. DEPARTMENT OF AGRICULTURE. 



curve 4 shows the steam pressures corresponding to the tempera- 

 tures. Curve 2 shows the gauge pressure, and curve 3 shows the 

 gas pressure, which is the difference between the gauge pressure and 

 the steam pressure at any given point. Endeavor was made to keep 

 the temperature curve a straight line, but sometimes the tempera- 

 ture would drop and then to reach the desired temperature the observer 

 would turn on full pressure of steam, which caused a rapid increase 

 in the gauge pressure and accounts for some of the bulges in the gas and 

 gauge pressure curves. Every 15 minutes readings were taken of the 

 temperature and pressure. Owing to the peculiar type of construc- 

 tion of the digesters and the position of the thermometer well, it was 

 necessary at the end of about two and one-half hours of cooking to 

 inject steam into the digester to make up for the liquor taken up by 



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Fig. 7.— Cooking curves for cooks 97 and 100. 1, temperature; 2, gauge pressure; 3, gas pressure; 4, steam 



pressure. 



the chips, or the liquor level would sink below the thermometer well 

 and not give the correct reading. This was done as uniformly as 

 possible for every cook. 



METHOD OF FINISHING COOK. 



With the composition of liquor and temperature changing each 

 time, a great deal of difficulty was experienced at first in knowing 

 when to finish cooks so that each one would be pulped to the same 

 degree. The digester was equipped so that cold liquor for sampling 

 could be obtained by passing it through a condenser. 



An attempt to finish cooks to the same sulphur dioxide content 

 was made, but some would be overcooked while others would be 

 almost raw, as a result of using liquor containing different amounts 

 of S0 2 . This method can only be used when the same kind of liquor 



